The objectives of this research are to: (1) determine, in vivo, the relative rates of solubility disintegration of currently used luting cements and the effect of powder liquid ratios on the durability of zinc phosphate and polycarboxylate cements; (2) use these data to evaluate the validity of proposed new in vitro solubility and disintegration tests. Little data is available with respect to in vivo disintegration of luting cements and there is not complete agreement among the few studies that do exist. The in vivo disintegration rates of zinc polycarboxylate, glass ionomer, improved zinc oxide-eugenol and zinc silicophosphate cements will be compared to that of zinc phosphate cement. The cements will be inserted on 0.8 mm wells, 4 on the mesial and 4 on the distal of cast full crowns. The crowns will be temporarily cemented in the mouth, removed at 6 months and cement loss measured. They will be recemented for an additional 6 months when the loss of material again will be determined. Concurrently a series of laboratory solubility tests will be conducted using water and dilute organic acid of pH 4 and pH 2.5. Degradation will be determined by loss of cement from cement in 0.8 mm holes in plastic blocks, weight change of 0.5 mm thick discs, by change in transverse strength of 0.5 mm thick cement beams and change in area of cement films held between glass plates. All tests will be longitudinal in nature.